JSON for Modern C++ 3.8.0

accept
accept
accept
allocator_type
array
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at
at
at
at
at
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back
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basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
basic_json
begin
begin
binary
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end
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front
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~basic_json
| ## ◆ operator[]() [1/8]
reference nlohmann::basic_json::operator[] | ( | const json_pointer & | ptr | ) |
| inline
  Uses a JSON pointer to retrieve a reference to the respective JSON value. No bound checking is performed. Similar to operator[](const typename object_t::key_type&), `null` values are created in arrays and objects if necessary. In particular: If the JSON pointer points to an object key that does not exist, it is created an filled with a `null` value before a reference to it is returned. If the JSON pointer points to an array index that does not exist, it is created an filled with a `null` value before a reference to it is returned. All indices between the current maximum and the given index are also filled with `null`. The special value `-` is treated as a synonym for the index past the end. Parameters
  [in] | ptr | a JSON pointer
  Returns reference to the element pointed to by ptr Complexity Constant. Exceptions
  parse_error.106 | if an array index begins with '0'
  parse_error.109 | if an array index was not a number
  out_of_range.404 | if the JSON pointer can not be resolved
  Example The behavior is shown in the example. 1 #include <iostream> 2 #include <nlohmann/json.hpp> 3 4 using json = nlohmann::json; 5 6 int main() 7 { 8 // create a JSON value 9 json j = 10 { 11 {"number", 1}, {"string", "foo"}, {"array", {1, 2}} 12 }; 13 14 // read-only access 15 16 // output element with JSON pointer "/number" 17 std::cout << j["/number"_json_pointer] << '\n'; 18 // output element with JSON pointer "/string" 19 std::cout << j["/string"_json_pointer] << '\n'; 20 // output element with JSON pointer "/array" 21 std::cout << j["/array"_json_pointer] << '\n'; 22 // output element with JSON pointer "/array/1" 23 std::cout << j["/array/1"_json_pointer] << '\n'; 24 25 // writing access 26 27 // change the string 28 j["/string"_json_pointer] = "bar"; 29 // output the changed string 30 std::cout << j["string"] << '\n'; 31 32 // "change" a nonexisting object entry 33 j["/boolean"_json_pointer] = true; 34 // output the changed object 35 std::cout << j << '\n'; 36 37 // change an array element 38 j["/array/1"_json_pointer] = 21; 39 // "change" an array element with nonexisting index 40 j["/array/4"_json_pointer] = 44; 41 // output the changed array 42 std::cout << j["array"] << '\n'; 43 44 // "change" the array element past the end 45 j["/array/-"_json_pointer] = 55; 46 // output the changed array 47 std::cout << j["array"] << '\n'; 48 } Output (play with this example online):
      1
      "foo"
      [1,2]
      2
      "bar"
      {"array":[1,2],"boolean":true,"number":1,"string":"bar"}
      [1,21,null,null,44]
      [1,21,null,null,44,55]
  The example code above can be translated with
      g++ -std=c++11 -Isingle_include doc/examples/operatorjson_pointer.cpp -o operatorjson_pointer
Since version 2.0.0 Definition at line 23656 of file json.hpp.

nlohmann::json
basic_json<> json
default JSON class
Definition: json.hpp:2774